Plastic closures molded from thermoplastic polymeric materials have met with wide spread acceptance in the marketplace for use on containers having beverages and like products. Closures of this type, which can be efficiently formed by compression molding or injection molding, are typically configured for threaded application to associated containers, and are further configured to engage and cooperate with the container to effectively seal the container's contents. Closures of this type may be configured as so-called composite closures, including an outer closure shell, and an inner sealing liner, or as so-called “linerless” closures, wherein the closure shell itself is configured to provide the desired sealing cooperation with the associated container.
While closures of the above type have been very commercially successful, versatile use is promoted by enhancing the sealing and the structural performance of such closures, while at the same type minimizing the quantity of polymeric material required for formation of each molded closure.
Another desirable feature of closures of the above type relates to configuring the closures for tamper-resistance, that is, configuring each closure so as to provide visually discernable and/or audible evidence of partial or complete removal of a closure from an associated container. Typically, closures of this type provide tamper evidence by a section of a side wall or skirt portion of the closure that is easily separable from the main body of the closure. This separable feature is often referred to as the tamper band. The tamper band is typically molded as part of the main body of the closure, but is at least partially detachably connected to the closure by a plurality of frangible connections. These connections (sometimes referred to as leaders or bridges) are designed to provide sufficient strength to avoid disconnection or other damage during de-molding, transportation, and closure application, while being sufficiently weak as to reliably fracture, break, or otherwise deform attendant to removal of the closure from a container by consumers.
An important aspect of tamper band design is a feature intended to permit the tamper band of the closure to be irreversibly applied to an associated container, but to become visibly damaged when the closure is partially or completely removed. Those skilled in the art are familiar with “one-way” features, typically provided in the form of “tabs”, “wings”, or “nibs”. During closure application, these features are “snapped” or otherwise fitted over a mating feature on the container, typically referred to as the “A” diameter. This “A” diameter is a ring that protrudes radially outwardly from the container neck under which the “one-way” feature of the closure tamper band is retained.
Axial clearance (sometimes referred to as “drop space”) must be provided between the open end of the tamper band and the “A” diameter feature to allow the separated tamper band to drop away from the remainder of the closure, so that separation is obvious to the consumer. However, a drawback of such designs is that the closure and tamper band can be manipulated in an unauthorized fashion to defeat the tamper-evident function of the tamper band. One manner of defeating the tamper-evidence function entails inserting fingernails or an implement under the tamper band, in the “drop space” between the tamper band the “A” diameter feature of the container, and subsequently removing the closure from the container, either with or without relative rotation of the closure with respect to the container. By manipulation in this fashion, sufficient force can be generated at the open end of the tamper band such that the “one-way” features “such as tabs or wings” will be defeated, either by pulling them out and away from the “A” diameter feature, or by causing them to flip down or bend out of the way.
In view of the above design considerations, it is desirable to provide a plastic closure exhibiting enhanced sealing and structural performance, as well as enhanced tamper-resistance.